It is well known that a transformer converts electricity at one voltage to electricity as another voltage, either of higher or lower value. A transformer achieves this voltage conversion using a primary coil and a secondary coil, each of which is wound on a ferromagnetic core and comprises a number of turns of an electrical conductor. The primary coil is connected to a source of voltage and the secondary coil is connected to a load. The ratio of turns in the primary coil to the turns in the secondary coil (“turns ratio”) is the same as the ratio of the voltage of the source to the voltage of the load. Two main winding techniques are used to form coils, namely layer winding and disc winding. The type of winding technique that is utilized to form a coil is primarily determined by the number of turns in the coil and the current in the coil. For high voltage windings with a large number of required turns, the disc winding technique is typically used, whereas for low voltage windings with a smaller number of required turns, the layer winding technique is typically used.
A layer winding technique is disclosed in U.S. Pat. No. 6,221,297 to Lanoue et al., which is assigned to the assignee of the present application, ABB Inc., and which is hereby incorporated by reference. In the Lanoue et al. '297 patent, alternating sheet conductor layers and sheet insulating layers are continuously wound around a base of a winding mandrel to form a coil. The winding technique of the Lanoue et al. '297 patent can be performed using an automated dispensing machine, which facilitates the production of a layer-wound coil.
A transformer with layer windings may be dry, i.e., cooled by air as opposed to a liquid dielectric. In such a dry transformer, the windings may be coated with, or cast in, a dielectric resin using vacuum chambers, gelling ovens etc. If the windings are cast in a solid dielectric resin, cooling issues are raised. Cooling ducts have been provided in layer wound coils.
The larger the transformer and higher output rating, the greater the width of the conductor sheet is required or larger amount of conductor used. One cannot wind a conductor sheet above 48 inches on existing equipment.
Thus, there is a need to provide a coil for a transformer, with the coil having split coil segments with cooling ducts.